Corrugation or embossing is a conventional means of increasing the stiffness and the resistance against bending of comparatively thin materials in at least one direction. The technique is used in a variety of applications. For example may be mentioned corrugated sheet iron. Corrugated board is another example, as according to DE-A1-2 211 925. Also in nature there are many shapes where folding patterns and the like give increased stiffness. It is in these examples often the question of comparatively thin materials, i.e. blades on flowers and grass, etc.